JPH0226992B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to electronic cardiac pacemakers, and more particularly to an atrial synchronized pacemaker or an electronic cardiac pacemaker capable of operating in an atrial synchronized mode.
This invention relates to an R-wave suppression pacemaker.

Atrial synchronized pacemakers are designed for use in patients whose heart exhibits normal atrial self-pacing, but there is a defect in conduction from the atria to the ventricles so that the ventricles do not beat or the ventricles are out of sync with the atrial rhythm. has been done. Atrial synchronized pacemakers are designed to sense naturally occurring atrial contractions (depolarizations) and deliver electrical stimulation pulses to the ventricle at the end of a short time interval to induce ventricular contraction. The time delay interval is selected so that atrial and ventricular contractions are synchronized with a suitable delay interval to provide effective pumping. Atrial-gated pacing attempts to replace the lack of natural conduction of stimulation pulses from the atria to the ventricles in the heart, but allows the heart rate, within certain limits, to follow the natural rhythm established by self-pacing of the patient's atria. Follow freedom. Other features are often combined with atrial synchronized pacing, such as a rate ceiling or fixed rate pacing when the spontaneous atrial rate falls below a predetermined atrial rate. Devices known in the art may also be provided for programming pacemakers after implantation to adjust atrioventricular delay, high and low rates, and other operating parameters. If ventricular depolarization occurs subsequently in response to atrial depolarization,
A ventricular inhibition function may also be provided to sense ventricular depolarization and prevent the pacemaker from delivering competitive ventricular stimulation pulses. In this method, stimulation pulses are sent only when needed.

In addition to atrial synchronous pacemakers, other types of pacemakers that can operate in multiple modes include atrial synchronous operation as one possible mode of operation.
A dual-sense/dual-pace atrioventricular pacemaker, sometimes called a fully automatic pacemaker, can selectively send stimulation pulses to both the atria and ventricles; It can also operate as appropriate to maintain synchronicity. This fully automatic pacemaker works if the patient's atria are pacing on their own (thus inhibiting the delivery of atrial stimulation pulses) above the minimum rate, and the ventricles are able to pace themselves on their own after an atrial contraction. If it does not contract within a certain time interval, it operates in atrial synchronized mode. In this case, ventricular stimulation pulses are delivered at a selected atrioventricular delay interval after atrial contraction, resulting in atrial synchronization.

Pacemakers operating in atrial synchronized mode have the potential to cause ventricular stimulation pulses to be delivered at heart-beat cycle time intervals that are inappropriate and dangerous under certain circumstances. It is easy to make mistakes. This problem can occur when premature ventricular contractions occur before atrial contractions. Although the atrial sense amplifier is intended to respond only to atrial depolarization (P waves) in the electrocardiogram, R waves due to ventricular depolarization may actually be detected as P waves by the atrial sense amplifier. . This initiates the AV delay interval,
Following this, the pacemaker sends ventricular electrical stimulation pulses. This pulse occurs during the heart's vulnerable period during repolarization due to premature ventricular contractions.
This may occur. It is medically bad practice to send stimulation pulses during this period of vulnerability. This is because such pulses can be dangerous to the patient in certain situations since they can cause fibrillation of the heart.

It begins with premature ventricular contractions and enters the vulnerable phase.
It is recognized in the prior art that the sequence of events described above, in which ventricular stimulation pulses are delivered during period), is unwelcome, and various solutions have been proposed. In an attempt to suppress premature ventricular contractions so that they are not detected by the atrial sensing circuitry, drug therapy has been shown to cause premature ventricular contractions (atrial-triggered ventricular contractions).
have been used in conjunction with pacemakers (synchronous ventricular pacemakers). However, drug therapy has limitations and may be ineffective or inappropriate in certain situations and for some patients. Electronic filtering is used in conjunction with an atrial sense amplifier to distinguish between P and R waves and suppress R waves. However, filtration itself is not helpful or reliable in distinguishing between atrial and ventricular events. This is because there is an inherent difference in the shape and frequency composition of human R waves and P waves. Since some people's R waves are more similar to other people's P waves, any attempt to differentiate by electronic filtering becomes very complicated.

The present invention senses in both the atria and ventricles, and when operating in atrial synchronization mode, ventricular stimulation pulses are delivered only in response to actual atrial contractions and not in response to premature ventricular contractions. The above-mentioned problem is solved by taking timing considerations to distinguish between P waves and R waves so that they are not transmitted.

The present invention is useful with both unipolar and bipolar pacemakers, and is particularly useful with unipolar pacemakers. This means that in the prior art,
This is because distinguishing between P waves and R waves is more difficult in unipolar pacemakers. The preferred embodiment shown here is for a unipolar pacemaker.

According to the present invention, a pacemaker is provided for selectively delivering stimulation pulses to the heart in an atrial-gated mode of operation, the pacemaker including terminals for connection to both the ventricles and atria of the patient's heart. . Pulse generating means is provided for selectively delivering ventricular electrical stimulation pulses to the ventricles via the ventricular terminals. A ventricular sense amplifier is connected from the ventricular terminal and operates to sense the ventricular beats of the heart. The ventricular sense amplifier has a dead time or refractory time after sensing a ventricular beat or generating a stimulation pulse. an atrial sense amplifier is connected to the atrial terminal for sensing a P wave indicative of atrial depolarization, and a delay means operatively connected to the atrial sense amplifier detects a predetermined time interval after the sensed atrial depolarization. to trigger the generation of a ventricular electrical stimulation pulse. A control means is operatively associated with the atrial sense amplifier to cause the ventricular sense amplifier to inactivate the amplifier during the refractory time and to prevent the ventricular premature beat or other ventricular event from being activated by the atrial sense amplifier. to prevent it from being accidentally detected.

According to another aspect of the invention, the atrial sense amplifier is kept inactive during the ventricular sense amplifier refractory time and also for a predetermined time interval after the refractory time; The propagation time from the lower point to the atrial leads of the heart prevents delayed ventricular events from being detected. That is, the configuration of the present invention is as follows. The present invention provides: a ventricular terminal means connected to a patient's heart for sending ventricular stimulation pulses to the patient's heart; a pulse generating means for selectively sending a ventricular electrical stimulation pulse to the ventricular terminal means; and a pulse generating means connected to the ventricular terminal means. ventricular sense amplifier means connected to the patient's heart for sensing ventricular beats of the heart and having a refractory time after sensing a ventricular beat or a ventricular stimulation pulse; and an atrial terminal means connected to the patient's heart for sensing atrial beats. , atrial sense amplifier means connected to said atrial terminal means for sensing atrial contractions of the heart, and operatively connected to said ventricular sense amplifier means and said pulse generation means for a predetermined time interval after a sensed atrial contraction. and a control means operatively connected to disable said atrial sense amplifier means during a refractory time of said ventricular sense amplifier. an R-wave suppressed pacemaker for selectively delivering stimulation pulses to the heart in an atrial synchronized mode of operation, further comprising: the control means operatively controlling the atrial and ventricular sense amplifier means; and in response to a sensed atrial or ventricular beat, during an atrial refractory time that begins with the sensed atrial or ventricular beat and continues for a period of time after the end of the ventricular refractory time; The present invention relates to an R-wave suppression pacemaker characterized in that the atrial sense amplifier is not activated.

Preferred embodiments will be described in detail below.

FIG. 1 shows a block diagram of the major functional elements of a pacemaker incorporating the present invention. Pacemakers can be external or implantable, and in either case are connected to the patient's heart through electrical leads. Reference numeral 10 graphically represents the patient's heart. The conductor 11 extends into the atrium, the upper compartment of the heart, and the conductor 11 has an electrode 12 in contact with the heart in the atrium. Similarly, conductor 1
3 has an electrode 14 which extends into the ventricle, ie into the lower compartment of the heart, and whose end contacts the heart in the ventricle. The diagram shows two separate conductors 1
1 and 13, however, as is generally known in the art, a single multi-conductor wire with separate electrodes at one location on the tip and one side of the conductor may be used for contacting the ventricles and atria. good. Leads 11 and 13 connect to terminals 15 and 16, respectively, provided on the pacemaker housing for connection to various components and circuits within the pacemaker.

A pulse generator 20 is included within the pacemaker. Pulse generator 20 is operative to selectively generate electrical cardiac stimulation pulses at its output 21, which output 21 is connected to terminal 16 via conductor 22 so that the generated output pulses are connected to the ventricular chambers. conducted to. When operating in the atrial synchronization mode, pulse generator 20 delivers output pulses in response to an input signal at its trigger input 23. Pulse generator 20 preferably also has a backup mode to cause the heart to beat at a minimum rate if no trigger pulses are received or if trigger pulses occur below the minimum rate. In any event, when a reset pulse is applied to its reset input 24, it is inhibited from sending an output pulse. The specific circuitry suitable for the function of pulse generator 20 described above is generally known in the art and will not be described in detail here. It is also generally known in the art that the minimum rate at which switching to backup mode occurs can be adjusted by program input from a radio frequency programming device as known in the art.

A branch of conductor 22 is input 3 of ventricular sense circuit 30.
Connected to 1. The ventricular sense circuit 30 includes an amplification and filtering circuit, designated by the reference numeral 32, as commonly known in the art for detecting ventricular depolarization (QRS waves) in an electrocardiogram of a patient's heart indicative of ventricular contraction. Contains wave equipment. When a ventricular contraction is detected, a signal indicating the same is sent to the ventricular sense circuit 30.
is given in the output of Sense amplifiers used in pacemakers typically experience a dead time for a period of time after detecting a cardiac contraction or applying a generated stimulation pulse. During this dead time, referred to as the refractory time, the amplifier is temporarily "off", ie, does not sense any signal applied to its input. This refractory condition causes "ringing" or rapid pulse triggering, which may occur immediately after a contraction, and which, when sensed and amplified, may provide an input that conveys unnecessary or erroneous information to the pacemaker logic. This is useful in that it is not detected by the amplifier. To some extent, the refractory conditions after the input signal may be inherent to the particular electronic design of the filter and amplifier, depending on the component selection and the bias conditions of the usually very weak currents. temporarily disturbs the quiescent point and renders the circuit insensitive for a certain recovery time. Alternatively, specific timing or blanking circuitry can be included with the sense amplifier or filter to render the sense circuitry refractory for a specifically selected time after detection of a ventricular event. In Figure 1, reference numeral 34 indicates a dead time timer, which may be a separate timing circuit as suggested in the figure, or simply a dead time inherent in the sense amplifier and filter design. Good things will be understood. The method of characterizing refractory time timing by separate blocks in FIG. 1 should not be construed as being limited to separate timing means for refractory times.

An atrial sense circuit 40 is provided having an input 41 connected to the atrial terminal 15 via conductor 17. Atrial sense circuit 40 connects terminal 43 in response to detection of the P wave portion of the heart's electrocardiogram indicative of atrial contraction.
reference numeral 4 operating to give an output at
2, including the amplifier and filter shown at 2. As mentioned above, filters may be included in an attempt to distinguish between P and R waves, but such filtering may not always be reliable as the properties of P and R waves vary from patient to patient. do not have.

Atrial sense amplifier amplifier and filter 42 may be of conventional design generally known in the art;
However, in accordance with the present invention, a specific refractory time or dead time is provided for the atrial sense circuit. Although the atrial refractory time can be controlled by component selection and operating point selection for the sense amplifier electronics, a separate refractory time timing control circuit is provided in the preferred embodiment. This may take the form of a digital timer, or it may be an analog timing circuit such as a monostable multivibrator or its equivalent. When a signal is detected by the sense amplifier and filter 42, an output signal indicative thereof is provided at output 43. At the same time, a signal is provided via conductor 45 and OR gate 46 to input 47 of refractory timer 44.
Refractory time timer 44 then controls amplifier and filter circuit 42 via control line 48 to render them insensitive to the input signal for a refractory period while timer 44 is timing out. . This may be accomplished through appropriate gates, switch circuits or clamp circuits within or attached to the sense amplifier or input circuit.

Another input is provided to the OR gate 46 to render the atrial sense circuit 40 refractory; this input is provided by the branch of conductor 35 connecting from the output 33 of the ventricular sense circuit 30. The function of this connection is to ensure that the atrial sense circuit 40 is turned off or refractory at the same time as the ventricular sense circuit 30;
The purpose is to be able to distinguish between atrial and ventricular events, as detailed below.

Output 43 of atrial sense circuit 40 connects to input 51 of atrioventricular delay timer 50 via conductor 48 . Timer 50 may be a digital or analog timing circuit and functions to receive an input signal at its input 51 and then provide an output signal at its output 52 at predetermined time intervals. This output signal is sent via conductor 53 to trigger input 23 of pulse generator 20. Atrioventricular delay timer 50 provides a delay time interval between atrial contractions to allow the ventricles to fill with blood before the ventricles contract. A typical atrioventricular delay interval is approximately 120 milliseconds, and equipment generally known in the art is provided for programming a timer at input 54 to select the delay interval.
A signal from the ventricular sense circuit 30 activates the atrioventricular delay timer 5 to reset or cancel an interval that is being timed out by the atrioventricular delay timer 50.
0 also has a reset input connected to a branch of conductor 35.

When the pacemaker shown in Figure 1 operates in atrial synchronization mode, the spontaneous atrial contraction is a depolarization (P wave).
, which is extracted by the electrodes and sent via lead 11, terminal 15 and conductor 17 to input 41 of atrial sense circuit 40. The P-wave is detected and amplified to provide an output at 43 which is sent to an input 51 of an atrioventricular delay timer 50.
This initiates the timing of the atrioventricular (AV) delay interval. At the end of the atrioventricular delay interval, the output signal at output 52 is applied to trigger input 2 of pulse generator 20.
3 to cause pulse generator 20 to deliver ventricular output stimulation pulses to the heart via conductor 22, terminal 16, lead 13 and electrode 14. If a spontaneous ventricular contraction occurs after an atrial contraction and before the atrioventricular delay timing 50 times out,
Such ventricular contractions are detected by their depolarization (R-wave) transmitted via lead 13, terminal 16 to ventricular sense circuit 30. The R-wave is then detected and amplified to provide an output at 33 which is sent by conductor 35 to reset the atrioventricular delay timer 50 and pulse generator 20 for that heartbeat cycle. Output pulses are not required, so they are not generated.

Atrial synchronized pacemakers are typically equipped with a backup mode. When the heart rate falls below a preselected or programmed minimum heart rate, the pulse generator 20 returns to a mode in which it delivers ventricular stimulation pulses at the minimum heart rate, which does not include naturally occurring ventricular contractions. is detected by the ventricular sense circuit 30, there is a condition for resetting and inhibiting.

An important feature of the present invention is the control of the refractory or dead time of the atrial and ventricular sense circuits. As mentioned above, ventricular events such as R-waves or stimulation pulses cause the ventricular sense circuit 30 to be turned off or unresponsive for a period of time. Similarly, atrial sense circuit 4
When an event is detected by 0, the circuit is turned off or unresponsive for a certain period of time. In the preferred embodiment, refractory time timer 44 controls the refractory time of atrial sense circuit 40 and atrial sense amplifier 42.
When an event is detected by
4 and start the refractory time. Additionally, the output from the ventricular sense circuit 30 is connected to an OR gate 46.
is coupled to a refractory time timer 44 for the atrial sense circuit 40 via a conductor 35 that connects to an input of the atrial sense circuit 40 . Refractory time timer 44 is retriggerable, so that an input signal at input 47 starts a time and if further input is received during that time, refractory timer 44 is reset to expire its timeout. Start again. Ventricular sense circuit 30
is connected to the atrial refractory timer 44 to ensure that a ventricular event turns off the atrial sense circuit 40. This is important in distinguishing between R and P waves that are extracted by the atrial conductor and appear at the input of the atrial sense amplifier.

Because the electrical signals associated with ventricular events are relatively strong, ventricular events can be detected in both atrial and ventricular leads. However, the electrical P-wave signal associated with atrial contractions is relatively weak and localized, so it may only be detected by the atrial leads. Therefore, if the signal occurs in both the atrial and ventricular leads, it is a signal of ventricular origin, but if the signal occurs only in the atrial lead, it can be assumed that it is an atrial origin. It will be done. However, this assumption assumes that both sense amplifiers operate continuously. A premature ventricular contraction is detected by the atrial amplifier if it occurs during the refractory time of the ventricular amplifier, thus leading to the problems seen in the prior art described above.

The present invention solves this problem by maintaining constant operating conditions with respect to the on or off state of the sense amplifier. The first condition is that a ventricular event, either a spontaneous ventricular contraction or a ventricular stimulation pulse, causes both the atrial sense amplifier and the ventricular sense amplifier to be in an off or refractory state. The second condition is that the atrial sense amplifier is turned on only when the ventricular amplifier is known to be active. Therefore, premature ventricular contractions that occur during the refractory time of the ventricular sense amplifier will not be falsely detected by the atrial sense amplifier as an atrial event, resulting in a vulnerable period of the heart as described above. The risk of stimulation pulses being delivered during the period) is avoided.

In the preferred embodiment, the output from the ventricular sense amplifier 32 is used to turn off the atrial sense circuit 40 by starting or resetting the refractory time timer 44 of that circuit. The time for the refractory time timer 44 is selected in conjunction with the specific refractory time of the ventricular sense circuit 30, or with that particular refractory time timing circuit, if present, so that the atrial sense amplifier 42
Ventricular sense amplifier 32 will not return to its on state until ventricular sense amplifier 32 also returns to its on state.

The timing relationships of the various signals and sensing times are illustrated in the timing chart of FIG. 2A, which shows the signals appearing in the atrial and ventricular leads at approximately the time of two beats, and the pacemaker's atrial sense of FIG. Amplifier 42, ventricular sense amplifier 32
and the state of the atrioventricular delay timer 50. The horizontal axis represents time starting from 0 and ending at approximately 1200 milliseconds.
To illustrate, Figure 2A shows two heart beat cycles, each with atrial synchronous operation, with the first cycle delivering a stimulation pulse and the second cycle at an appropriate time interval after the atrial contraction. This shows that spontaneous ventricular contraction occurs.

At time 0, a P wave occurs in the atrial lead. This has two effects. That is,
This initiates the atrioventricular delay time interval and also places the atrial sense amplifier in an off or refractory state. In the preferred embodiment, the atrioventricular delay time is 120 milliseconds. After 120 milliseconds have elapsed, the R wave indicating ventricular contraction has not been received, so the pulse generator 20 sends a stimulation pulse to the heart. When this pulse occurs, it induces a corresponding signal in the atrial lead, but since the atrial sense amplifier 42 is turned off, this signal is not detected. In FIG. 2A, the effect of the ventricular stimulation pulse on the atrial lead is shown as a dotted spice. As the ventricular pulse is sent, it is detected by the ventricular amplifier,
The ventricular amplifier enters a refractory time. The ventricular sense amplifier also resets the refractory time timer 44 for the atrial sense amplifier, as shown at reference numeral 56, and restarts the atrial refractory time.

After the ventricular stimulation pulse, the atrial sense amplifier and atrial sense amplifier remain off. After approximately 140ms, the ventricular sense amplifier returns to its on state, but the atrial sense amplifier remains off for an additional 30ms, or 170ms after the ventricular pulse resets it. . Therefore, the atrial sense amplifier in the preferred embodiment is used not only during the refractory time of the ventricular sense amplifier, but also for reasons discussed below in connection with FIG. 2B.
It remains off during the 30ms overlap.

In FIG. 2A, after both the ventricular and atrial sense amplifiers are turned back on, the pacemaker waits for the next signal from the heart. Assuming that the heart's natural atrial pacing is working normally, a P wave is then detected at the atrial sense amplifier at approximately 800 ms in FIG. 2A. This again starts the atrioventricular delay timer and turns off the atrial sense amplifier. In this example, it is assumed that normal conduction is occurring in the heart and that ventricular contraction occurs before the end of the atrioventricular delay time. The R wave is shown on the ventricular leads in Figure 2A at approximately 900 ms and resets or terminates the atrioventricular delay time, initiates the ventricular sense amplifier refractory time, and resets the atrial sense amplifier refractory time. let After another 140 ms, the ventricular sense amplifier turns back on, and after another 30 ms, the atrial sense amplifier turns back on.

The first step is to eliminate the possibility of falsely detecting premature ventricular contractions (PVCs) as atrial contractions.
This is clear from consideration of the circuit shown in the figure and the operation timing chart of FIG. 2A. If it occurs during the off-time of the sense amplifier, it will only be ignored by the pacemaker, and if it occurs during the on-time of the atrial sense amplifier, it will be ignored by the pacemaker according to the present invention. It always happens between hours. If a PVC occurs while the ventricular amplifier is on, regardless of whether the atrial amplifier is on, the atrioventricular delay timer is reset or canceled so that the stimulation pulse is
Not sent in one atrioventricular delay interval after PVC.

For the reasons discussed above, it proves important that the atrial sense amplifier is not turned on until the ventricular sense amplifier is also turned on. Additionally, it is preferred that the turn-on of the atrial sense amplifier is delayed by a short period of time after the turn-on of the ventricular sense amplifier. This can be seen more clearly with the help of Figure 2B. In FIG. 2B, the atrial and ventricular lead signals and the on or off states of the atrial and ventricular sense amplifiers are shown as in FIG. 2A. However, because the expanded scale is used in FIG. 2B, the 30 ms overlap time between ventricular sense amplifier turn-on and atrial sense amplifier turn-on appears even more pronounced. Therefore, FIG. 2B only shows a portion of the heartbeat cycle corresponding to a range of about 250-350 ms after P-wave sensing. For convenience of illustrating the purpose of overlap, there are four specific times t _w ~
It is displayed as t _z . Time t _x is the end of the ventricular refractory time, which in the preferred embodiment is 140 ms after the ventricular event. Time _tz is the end of the atrial sense amplifier refractory time, which in the preferred embodiment is 170 ms after the ventricular event resets the atrial refractory time timer.

Now, suppose that a PVC occurs just before the ventricular sense amplifier turns on, ie, at time _tw . Of course, if the PVC occurs immediately after the ventricular sense amplifier turns on, the pulse generator and atrioventricular delay timer are reset as described above, eliminating any possibility of an inappropriate pacemaker response. However, if the PVC occurs just before the ventricular sense amplifier turns on, the PCV will not cause the reset operation as described above. If the atrial sense amplifier were to turn on at the same time as the ventricular amplifier at time _t is not detected. For example, if a PVC occurs in the lower atrium, there may be a short but significant time delay for the electrical signal generated by the PVC to propagate to the atrium, where it is picked up by the atrial conductors. Conducted to the atrial sense amplifier. If both amplifiers are turned on at the same time, a PVC that occurs just before turn on can be detected only by the atrial lead, and the signal is then interpreted as an atrial event, one atrioventricular delay time interval. Trigger the atrioventricular delay timer and pulse generator after. Of course, in such a situation, stimulation pulses may occur during the heart's vulnerability period after the initial PVC.

To eliminate this possibility, in the preferred embodiment, the atrial sense circuit is kept off for a period of time, referred to as overlap, after the refractory time of the ventricular sense circuit has elapsed. In the preferred embodiment, this overlap is 30ms.
Therefore, the atrial sense circuit operates at time t _z in Figure 2B.
It will not turn on until. Therefore, the propagation delay PVC that occurs in the atrial conductor at time t _y still occurs within the refractory or off time of the atrial sense amplifier and is therefore ignored. This time interval of 30 ms was chosen to provide a safety margin to prevent the above-mentioned concerns, while being short enough not to interfere with consideration of the maximum pacing rate for the pacemaker.

Referring to FIG. 3, an alternative embodiment of a cardiac pacemaker according to the present invention is shown. The embodiment of FIG. 3 is similar in many respects to the embodiment of FIG.
The same reference numerals are used for corresponding elements in FIGS. 1 and 3. The main difference in FIG. 3 compared to FIG. 1 is the use of a refractory time flip-flop 60 and an atrial overlap timer 61 in place of the refractory time timer 44 of FIG.

Specifically, OR gate 46, whose output is connected as in FIG. 1, has an output connected to one input of refractory time flip-flop 60. This input is labeled "Start" in FIG. The other input to flip-flop 60, labeled "Stop" in FIG.
Connected from the output of Conductor 48 connects from flip-flop 60 and controls the blanking or refractory time of atrial sense amplifier 42.

Input to atrial overlap timer 61 is provided via lead 62 from refractory time timer 34A. In the embodiment of FIG. 3, refractory time timer 3
4A is a special timing circuit that controls the refractory time of the ventricular sense amplifier 32. When amplifier 32 detects a ventricular event, it starts timer 34A, which blanks amplifier 32 for the selected refractory time. At the end of the timeout period of timer 34A, the blanking signal is removed from amplifier 32, returning the amplifier to the ready state. At the same time, the removal of the blanking signal triggers the atrial overlap timer 61 to start timing. The input from the timer 61 is designed to be triggered on the upstream section of the blanking signal from the timer 34A.
starts timing when timer 34A finishes timing.

The operation of the embodiment of FIG. 3 is similar to that of FIG. The atrial sense amplifier enters its refractory time in response to sensing an atrial event or sensing a ventricular event. An atrial event sensed on lead 45 is sent to gate 4
6 to switch flip-flop 60 and its output on conductor 48 to amplifier 42.
blank. Alternatively, a ventricular event causes flip-flop 60 to blank amplifier 42 with a signal on conductor 35 coupling through gate 46. In either case, the amplifier 42
It remains refractory until a predetermined overlap time after the ventricular sense amplifier refractory time expires. When amplifier 32 is turned back on after timer 34A times out, atrial overlap timer 61 is triggered, causing an overlap timer time delay. This time delay is approximately 30 ms, as discussed above in connection with FIG. At the end of the overlap time, timer 61 sends a signal to flip-flop 60 to switch it to remove the blanking signal from conductor 48 and atrial sense amplifier 4.
Turn 2 back on. Figure 2A and Figure 2B
The operations described above in connection with this also apply to the operation of the embodiment of FIG.

The present invention turns off the atrial sense circuit when an atrial event occurs, and maintains the circuit off, preferably until after, but in no case before, the ventricular sense amplifier returns to the on state. Therefore, inappropriate due to the generation of PVC,
It will be understood from the above description that the transmission of potentially dangerous stimulation pulses is also prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a cardiac pacemaker according to the present invention. 2A and 2B are waveform graphs showing the operation of the pacemaker of FIG. 1. FIG.
FIG. 3 is a block diagram similar to FIG. 1 of an alternative embodiment of a pacemaker according to the invention. 20: pulse generator, 30: ventricular sense circuit,
34: refractory time timer, 40: atrial sense circuit,
44: refractory time timer, 50: atrioventricular delay timer,
60: Refractory time flip-flop, 61: Atrial overlap timer.

Claims (1)

[Scope of Claims] 1. Ventricular terminal means connected to the patient's heart and sending ventricular stimulation pulses to the patient's heart; Pulse generating means selectively sending ventricular electrical stimulation pulses to the ventricular terminal means; and the ventricular terminal means. a ventricular sense amplifier means connected to the patient's heart for sensing ventricular beats of the heart and having a refractory time after sensing a ventricular beat or a ventricular stimulation pulse; and an atrium connected to the patient's heart for sensing an atrial beat. terminal means; atrial sense amplifier means connected to said atrial terminal means for sensing atrial contractions of the heart; and operatively connected to said ventricular sense amplifier means and said pulse generation means to detect a predetermined period of time after a sensed atrial contraction. a delay means for generating a ventricular electrical stimulation pulse after a time interval of , and a control means operatively connected to disable said atrial sense amplifier means during a refractory time of said ventricular sense amplifier. An R-wave suppressing pacemaker that selectively sends stimulation pulses to the heart in an atrial synchronization mode. 2. said control means is operatively connected to said atrial and ventricular sense amplifier means and responsive to a sensed atrial or ventricular beat, said control means starts with a sensed atrial or ventricular beat and starts said ventricular sense amplifier means; 2. The R-wave suppressed pacemaker according to claim 1, wherein said atrial sense amplifier is not activated during an atrial refractory time that continues for a certain period of time after the end of the refractory time.